The present invention relates to the general field of so-called “passive” acoustic treatment.
The field of application of the invention is particularly, but not exclusively, the field of aviation turbine engines.
The use of passive acoustic treatment panels is frequent in the field of aviation for reducing noise emissions given off by turbine engines. For example, for a turbojet of the two-spool bypass type, such panels may be arranged on the inside face of the nacelle of the turbojet, and also on the inside and outside faces of its primary cover.
A passive acoustic treatment panel is generally in the form of a cellular honeycomb structure covered in a thin porous layer acting as a wall for the air-flow passage and closed at the other end by a layer that is reflective from an acoustic point of view (also referred to as a “solid” skin).
Panels that are more complex, with intermediate porous layers inserted between honeycomb structure layers may be provided in order to extend attenuation over a wider range of frequencies. By way of example, reference may be made to publication U.S. Pat. No. 3,948,346, which describes an example architecture for a two-layer acoustic panel having two cellular structures that are sandwiched between a solid skin and a perforated skin, and that are separated from each other by a metal sheet that is likewise perforated.
The two-layer acoustic treatment panel described in that document U.S. Pat. No. 3,948,346 possesses numerous drawbacks, such as being of relatively complex design, presenting considerable weight, and of having sub-optimal mechanical strength.